Process for dewaxing lubricant stocks



June 22,1943.

R. w. HENRY EIAL PROCESS FOR DEWAXING LUBRICANT STOCKS Filed May 9. 1940 CI: 5 -L :1

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combined actions may be accomplished in one "stage or step, but we may use more than one Patented June 22, 1943 PROCESS FOR DEWAXING LUBRICANT STOCKS Robert W. Henry, Bartlesville, and James V. Montgomery, Okmulgee, kla., and Shelby D.

Lawson.

Berger, Tex.,

assignors to Phillips Petroleum Company, a corporation of Delaware Application May 9, 1940, Serial No. 334,292

3 Claims.

This invention relates to an improved process for the dewaxing of mineral or other oils. More specifically, it relates to a process of solvent dewaxing of mineral oils and deoiling of the wax in which cold nuclei are provided to refrigerate the oil, aid in wax crystallization and assist in gravity separation of the wax crystals.

It is well known that solidified wax may be separated from an oil solution in a suitable solvent by cold settling, centrifuging, filtration, electrical precipitation, etc. But, the wax so separated contains adhering oil which reduces the yield of dewaxed oil as well as lowering the quality of the removed wax, unless the wax contaminated with oil is subjected to exhaustive washing or sweating, or is diluted with additional solvent, recrystallized by chilling the solution, and centrifuged, filtered or cold settled a second time.

In known dewaxing processes, difficulty is frequently experienced in inducing proper crystal formation and in controlling of the growth of the wax crystals, so that the subsequent settling or filtration of the crystals may be slow and washing incomplete.

We have found that the aforementioned difliculties may be remedied by a method of internal direct refrigeration combined with proper control of wax crystal growth along with efficient separation and washing of the wax, in which cold, immiscible, relatively finely divided solid or liquid materials are introduced into a solu- These stage, preferably three or more stages. By the use of said multiple stages the wax is removed in successive fractions and washed free of adhering oil in each step, as is more fully set forth below.

*The solvent may be any suitable dewaxing solvent known to the art, as liquefied normally gaseous hydrocarbons, light naphthas, gasoline, heavy naphthas or their derivatives, acetone-benzol, ethylene dichloride, picolines, mixtures of selective solvents with miscibility enhancers, etc., the principal reuqirement being that the solvent be completely miscible with the oil and wax at temperature of 100-120 F. and be completely mis- -cible with the oil at the dewaxing temperature with but little solubility for wax at the dewaxing temperature. The waxy oil is dissolved in a dewaxing solvent, as mentioned above, at a suitable temperature, usually above 100 F. and is introduced into a tower or other vessel, usually vertically arranged at a temperature just above that of substantial wax precipitation.

Near the top of this tower or column is introduced the chilled or cold immiscible, relatively finely divided solid or liquid material. These cold droplets, either solid or liquid, serve at first to cool the oil-solvent mixture to dewaxing temperatures, then serve as cold nuclei upon which wax may crystallize, thereby eliminating tendencies toward supersaturation or delayed wax separation. In one embodiment of our present invention we use chilled droplets of mercury as the refrigerant and these droplets falling through the waxy oil-solvent solution provide a cold metallic surface or serve as nuclei upon which crystallizing wax adheres. The cold mercury droplets, in addition to serving as a surface upon which the wax may precipitate, serve to induce wax crystal formation. Since an infinitely large number of chilled mercury droplets are added during the cooling and precipitation processes, the wax usually crystallizes in relatively small crystals, in which form the wax may be more readily settled and washed free of adhering oil. These wax-coated droplets, having a relatively high density, are carried downwardly by gravity through a column of upwardly flowing cold solvent which is introduced near the bottom of the tower, and the adhering oil is washed from the wax coated particles. These wax-mercury aggregates, substantially free of oil, are removed from the bottom of the tower, and may be separated into mercury and wax-solvent solution by warming and settling. The solvent may be separated from the wax-solvent solution in a stripping still and the solvent returned to the process. The chilled oil-solvent solution containing oil of desired pour point flows from the top of the tower, and the dewaxed oil is freed of solvent by known stripping methods.

The efiiciency of the operation may be maintained more nearly at the maximum by carefully controlling the extent of wax precipitation upon the particles of added liquid or solid, especially as regards size. The use of mercury droplets as the cold transfer medium is especially advantageous, since mercury an excellent conductor of heat and cold and since it may be readily broken up into small globules in the presence of oil. The extent of wax precipitation and the size of wax crystals may be controlled by control of the temperature of the mercury. For example, the greater the temperature diiferential between the mercury and the waxy solution the greater is the amount of heat absorbed by the mercury droplets in raising their temperature to that of the surrounding solution and the greater is the quantity of wax precipitated on the mercury droplets, and conversely the smaller the temperature differential between the waxy solution and the mercury droplets, the smaller will be the wax crystals in addition to a smaller amount of wax precipitated on each mercury droplet.

A composite particle made up of mercury with a small portion of wax will have a greater density and will settle or drop out more rapidly than a like droplet of mercury with a larger portion of wax. Similarly, smaller aggregates are more easily washed free of occluded oil than larger ones.

The removal of the mercury-wax particles from the oil-solvent solution and the washing of these aggregates by solvent may be effected by any known means, as by gravity settling and countercurrent washing as described herein, or by centrifugal or other suitable means.

Although mercury is described as the precipitant in the preferred embodiment of this invenlution provide nuclei upon which wax is precipitated in much the same manner as with droplets of mercury.

By the terms parafiin and wax the applicants:

intend to include that wax-like. non-asphaltic material which separates from crude or other mineral oils by cooling. The drawing shows the treating zone in the form of a tower and it is so described herein, but it will be obvious that the applicants process does not depend upon any particular form of apparatus.

Also in the discussion of our invention, mercury will be used as an example of a precipitant,

but other solids or liquids as described herein.

can be successfully employed.

It is, therefore, an object of our invention to separate parafiin and other waxy materials from 'parafiinic oils.

Another object of our invention is to eifect'a.,

sharp separation of waxy materials from paraffin'ic oils.

Still another object of this invention is to provide an efficient and convenient method of separating wax from a solution of wax-bearing oil.;

I successfully practicing our invention.

Example The figure is a diagrammatic elevation, largely in section, illustrating my improved dewaxing system.

One application of our process involves the use of droplets of mercury as a refrigerant, as nuclei for wax precipitation, and as a, settling aid. The

solvent may be any dewaxing solvent known to the art, such as heretofore enumerated, the principal requirement being that the solvent be completely miscible with the oil and wax at temperatures of approximately l00-120 F. and be completely miscible with the oil at dewaxing temperature with but little solubility for wax at the dewaxing temperature.

Referring to the figure, charge oil containing wax is dissolved in a suitable dewaxing solvent at 100 F. or over, in a mixer not shown, and the solution cooled to a temperature just above that of substantial wax precipitation, say 5 or 10 F. above this wax precipitation temperature, is transferred through line I into tower 2 near the mid-point of said tower. Near the bottom of this tower is introduced through line 3 said dewaxingsolvent which has been previously cooled to a temperature substantially the same as that of the contents of the tower at the point of introduction of the said dewaxing solvent, this cooling being done in chiller 4. The chilled oil-solvent solution passes upward through tower 2 and is met by and contacted with a downward flowing continuous stream of chilled mercury droplets to which precipitated paraliin wax is adhering. Said mercury droplets, introduced into the tower through line5, have been previously chilled in chiller ES. These chilled droplets of mercury falling through the waxy oil-solvent solution serve, first, to cool the said solution to a dewaxing temperature, then second, to provide a cold metallic surface to which the wax may adhere, and third, serve as Weighting material to assist the precipitated wax particles to settle more rapidly than they would without the use of said weighting material. These wax-coated particles, having a relatively high density, are carried downward through a column of upward flowing solvent, and the adhering oil is, washed from the wax. The wax and mercury substantially free of oil is removed from the bottom of the tower 2, through line I and may be freed of the mercury by warming and settling in separator 8. This mercury from said separator 3 is recycled by pump 9 through line It and chiller 5, thence through line 5 and into tower 2 for reuse. The solvent-wax solution exits from separator 3 through line I! and passes into still G2 in which the solvent is separated from the wax, which passes from the said still through line i3 to wax storage not shown. The separated solvent leaves still- I! through lines i l and i5, is cooled in cooler l6; and stored in surge storage tank ll, previous to recycling through the dewaxing zone.

The solvent-dewaxed oil solution leaves the dewaxing tower 2 through line 18, and is separated into wax-free oil and solvent in still IS. The dewaxed oil is drained from the still and transferred through line 20 to oil storage, not shown, and the solvent vapors leave the still through line 2! and join the solvent vapors from still l2 in line l5, and the combined streams of solvent proceed to recycle through the system as'above described.

It is obvious to those familiar with the art that this process can be applied in progressive stages and an increasingly higher melting point wax and lower pour point oil be taken from successive stages.

The temperature of the oil-solvent solution in the tower may be maintained constant or a temperature gradient may be maintained between the bottom and the top of the tower, or between the bottom of the first tower and the top of the next tower in a succession of towers in series.

The relative position at which line I enters tower 2 is selected from optimum operation.

It is to be understood that the above is merely illustrative of the principles and preferred embodiments of our improved invention of which many variations may be made by those skilled in the art without departing from the spirit thereof.

We claim:

1. The continuous process of dewaxing mineral oils including the steps of mixing the waxy oil with a dewaxing solvent at such a temperature as to have complete solution between the waxy oil and solvent, continuously passing chilled, relatively finely divided particles of liquid mercury in countercurrent relation to the waxy oilsolvent mixture and maintaining a temperature differential between the chilled liquid mercury droplets and the waxy oil-solvent mixture to chill the said mixture to dewaxing temperatures and to furnish chilled nuclei upon which the wax precipitates thereby forming relatively heavy wax-liquid mercury aggregates, and separating these aggregates from the oil-solvent mixture.

2. The continuous process of dewaxing mineral oils including the steps of mixing the waxy oil with a dewaxing solvent at such a temperature as to have complete solution between the waxy oil and solvent, continuously passing chilled, relatively finely divided particles of liquid mercury in countercurrent relation to the waxy oilsolvent mixture and maintaining a temperature differential between the chilled liquid mercury droplets and the waxy oil-solvent mixture to chill the said mixture to dewaxing temperatures and to furnish chilled nuclei upon which the wax precipitates thereby forming relatively heavy iii) wax-liquid mercury aggregates, and contacting the liquid mercury-wax aggregates in countercurrent relation with additional chilled dewaxing solvent to wash the said aggregates of cocluded oil and the more oily wax, and separating the less oily wax from the particles of liquid mercury, and separating the dewaxed oil from the solvent.

3. The continuous process of dewaxing mineral oils including the steps of mixing the waxy oil with a dewaxing solvent at such a temperature as to have complete solution between the waxy oil and solvent, continuously passing chilled, relatively finely divided particles of liquid mercury in countercurrent relation to the waxy oil-solvent mixture and maintaining a temperature differential between the chilled liquid mercury droplets and the waxy oil-solvent mixture to chill the said mixture to dewaxing temperatures and to furnish chilled nuclei upon which the wax precipitates thereby forming relatively heavy wax-liquid mercury aggregates, and contacting the liquid mercury-wax aggregates in countercurrent relation with additional chilled dewaxing solvent to wash the said aggregates of occluded oil and the more oily wax, and separating the less oily wax from the particles of liquid mercury, and separating the dewaxed oil from the solvent and recycling the liquid mercury and the dewaxing solvent.

ROBERT W. HENRY. JAMES V. MONTGOMERY. SHELBY D. LAWSON. 

